The rationale for this study was based on synergistic activity of AUY922 plus trastuzumab in the HER-2 positive BT-474 breast cancer xenograft model [28] and clinical experience of other HSP90 inhibitors in combination with trastuzumab in patients with advanced HER2-positive metastatic breast cancer progressing on trastuzumab [30]. This evidence concerns the gene ERBB2 and breast cancer.